We have used the methods of behavioral neurophysiology to study two major divisions of the frontal lobe of primates: the premotor cortex (PM) and the prefrontal cortex (PF). We completed the first phase of a study on motor learning by showing that PM cells dramatically change their activity while monkeys learn what motor act to execute on the basis of an arbitrary sensory stimulus. The ability to switch the behavioral significance of sensory stimuli in the short term underlies the flexibility of that characterizes the adaptation of advanced mammals to their rapidly changing but partially predictable environment. The next phase of our study of motor learning will involve an analysis of the circuits thought to be involved in the selection of behavior on some basis other than such arbitrary sensory stimuli. Two other aspects of this project have involved a contrast of the properties of PM and PF neurons. Our results support the hypothesis that PM plays a role in retrieving from motor memory the movement that needs to be made on the basis of a sensory event, but that PF is more involved in spatial analysis and other aspects of sensory information processing.